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As Lundin said, a 0 &Omega; resistor is for allowing an <i>optional</i> connection.  By the time you are laying out the board, you really should have a good grasp on the overall grounding and RF emissions strategy.  That would certainly include knowing whether the board ground plane will be connected to the chassis or not.

I would ditch the optional resistor.  It's not really a very good RF connection anyway.

With nothing needing to be soldered to the pad for the mounting screw, there is no point to add thermals.  Make sure to remove the screw pad from the paste layer so that it doesn't get covered with solder.  The screw will be solidly connected to the pad.  If the ground plane is the top layer, then the screw is connected to it directly.  If one of the other layers, then the screw is connected to it with a large-diameter via.  Either way should be better RF-wise than going thru a 0 &Omega; jumper.

If you want to disconnect the board from the chassis in testing the prototype, you can leave off the screw and put a piece of tape underneath, or use a nylon screw.

For lowest RF emissions, the board ground should be connected to the conductive chassis at one point only.  That point should be as close as possible to where external connections come thru the chassis onto the board.